Millennium is the third studio album (second in the United States) by American boy band Backstreet Boys, released by Jive Records on May 18, 1999. It was a highly anticipated follow-up to both their US debut album, and their second internationally released album. It was their first album to be released in both the US and internationally in the same form, at the same time.

Millennium held the record for most shipments in one year, with 11 million shipments sold in the United States in 1999. It was nominated for five Grammy Awards and became one of the best-selling albums of all time, selling 24 million copies worldwide. The Backstreet Boys promoted Millennium through the Into the Millennium Tour, which became one of the fastest-grossing tours of all time.